1. Field of the Invention
The present invention relates generally to the field of hydraulic mining, and in particular to mining thin slices of coal or other minerals deposits by means of water jets.
2. Statement of the Problem
Various types of water jets have long been used in the mining industry for the purpose of extracting mineral deposits by disrupting the mineral structure and forming a slurry of the resulting mineral particles. For example, large water jets, known as "giants" or "monitors," have been used in placer mining operations of precious metals for over a century. A good general history of hydraulic mining is provided by Frank, "Introduction to Hydraulic Mining and Jet Cutting" (BHRA Fluid Engineering, Cranfield, Bedford, England, 1976).
The room-and-pillar and longwall methods of mining are predominantly used in recovery of underground coal for seams ranging from 3 to 10 feet. In both methods, the entire seam is extracted in one pass. Mining of the complete seam in one pass is necessary to allow use of conventional mining equipment. Furthermore, this is conventionally thought to be the most efficient method of underground coal extraction. However, the roof of the excavated seam tends to be unstable and has been a major cause of fatality in the coal mining industry. The conventional approach to this problem has been to artificially support the mine roof by means of bolting, timbering, and/or hydraulic jacks. This imposes major economic constraints in mining operations by interrupting the continuity of the mining and haulage process and forcing the operation to become cyclic.
Hydraulic mining with water jets has been used for many years to extract coal deposits in China, Canada, Poland and the U.S.S.R. General reports concerning these efforts are provided by Kolesnikov, "Hydraulic Mining of Thick and Steep Coal Seams in the Soviet Union"; Parkes, "History of Hydraulic Mining at Kaiser" (both papers presented at the First International Symposium of Thick and Steep Seam Coal Mining, London, England, May 18-21, 1980); and by applicant's paper entitled "Status of Hydraulic Coal Mining in People's Republic of China" (Colorado School of Mines, Golden, Colorado). Further information in this area is provided in the treatise by Jeremic, Elements of Hydraulic Coal Mine Design (Trans Tech Publications, 1982).
However, under the prior art, water jets are used simply as a substitute for conventional cutting or excavating techniques in standard room-and-pillar, short wall, or long wall mining methods. The safety problems and economic constraints associated with providing artificial support for the mine roof have heretofore remained unsolved.
The most pertinent prior art reference appears to be U.S. Pat. No. 4,479,541 issued to the present applicant on Oct. 30, 1984 for "Method and Apparatus for Recovery of Oil, Gas and Mineral Deposits by Panel Opening." This patent disclosed a method and apparatus which employs panel openings to increase the surface area of drill holes to thereby enhance recovery of oil or gas. This method is also applicable to oil shale and tar sand recovery, as well as in-situ leaching of minerals such as uranium.
3. Solution to the Problem
Nothing in the prior art teaches or suggests use of a water jet to mine a series of thin horizontal slices of coal as taught by the present invention. Using conventional mining techniques, a mine roof can deflect elastically in the range of 6 to 12 inches and often as much as 2 to 3 feet or more with thin coal seams. By successively extracting thin horizontal slices of coal instead of the entire seam, the deflected mine roof will be supported by the remaining coal that forms the floor of the slices. Additional layers of horizontal slices can then be extracted from under the first layer of slices to maintain a gentle deflection and to preserve the integrity of the mine roof. This method substantially eliminates the need to provide artificial support for the mine roof. This method is also readily adaptable to remote control and automation which further reduces costs of production, and minimizes the risk of injury to miners.